The Magnetic Anomaly Map UK South is a colour contour map that shows variations in the magnetic field over the southern part of the UK landmass and adjacent sea area at a scale of 1: 625, 000. Magnetic contour values are displayed as total field anomaly. Magnetic anomalies show small departures from the expected value of the Earth’s magnetic field caused by variations in the magnetization of the rocks within the crust. The most prominent magnetic anomalies tend to be associated with igneous and metamorphic rocks that are exposed or occur at a shallow depth. The anomaly pattern becomes more subdued where these rocks are more deeply buried.